^r,  S.  LiBKARY.  Cop,  2.  M-  "^ 

THE  CONNECTICUT  ^o-  (  (p 

AGRICULTURAL  EXPERIMENT  STATION 

NEW  HAVEN,  CONN. 


/ 


BULLETIN  168,  JUNE,  1911. 


IMPROVEMENT    IN    CORN. 


By  H.  K.  Hayes  and  E.  M,  East. 


CONTENTS. 

Introduction 3 

The  Two  Results  Attending  the  Fornafetion  of  a  Seed 4 

What  Selection  Does 6 

Comparison  of  the  Effect  of  Selection  upon  Corn  and  upon  Tobacco, .  .  8 

The  Efifects  of  Inbreeding  upon  Corn 9 

Comparison  of  Pure  Lines,   Crosses  between  Pure  Lines  and  Nor- 
mally Cross-Fertilized  Varieties 11 

Comparison   between   Commercial   Varieties   and   First   Generation 

Hybrids  between  Them 13 

Method  of  Producing  Cross  Bred  Seed 18 


The  Bulletins  of  this  Station  are  mailed  free  to  citizens  of  Connecticut 
who  apply  for  them,  and  to  others  as  far  as. the  limited  edition  permit. 


Connecticit  Asricnltiral  Kiperlraeit  Station. 


OKPICERS    AND    STAFF 


BOARD  OF  CONTROL. 

His  Excellency,  Simeon  E.  Baldwin,  Ex  Officio,  Presidetit. 

Prof.  H.  W.  Conn,    Vice  President Middletown. 

George  A.  HopSon,  Secretary  ...............  Wallingford. 

E.H.Jenkins,  Director  and  Treasurer  . New  Haven. 

J.  W.  Alsop Avon. 

W.  H.  Lee Orange. 

Frank  H.  Stadtmueller  . Elmwood. 

James  H.  Webb Hamden. 


Administration 


STATION  STAFF. 
E.  H.  Jenkins,  Ph.  D.,  Director  and  Treasurer. 
Miss  V.  E.  Cole,  Librarian  and  Stenographer. 
Miss  L.  M.  Brautlecht,  Bookkeeper  and  Stenograt 


Chemistry. 

Analytical  Laboratory, 


John  Philips  Street,  M.  S.,  Chefuist  in  Charge. 
E.  Monroe  Bailey,  Ph.  D.,  C.  B.  Morrison,  B.  S.. 
R.  B.  Roe,  A.  B.,  C.  E.  Shepard,  Assistants. 
Hugo  Lange,  Laboratory  Helper. 
V.  L.  Churchill,  Sampling  Agent. 


Proteid  Research, 


T.  B.  Osborne,  Ph.  D.,  Chemist  in  Charge. 
Miss  E.  L.  Ferry,  A.  B.,  Assistant. 
Miss  Luva  Francis,  Stenographer. 


Botany. 


G.  P.  Clinton,  S.  D.,  Botanist. 

E.  M.  Stoddard,  B.  Agr.,  Assistant. 

Miss  M.  H.  Jagger,  Seed  Analyst. 

Miss  E.  B.  Whittlesey,  Herbari^mi  Assistant. 


Entomology. 


W.  E.  Britton,  Ph.  D.,  Entomologist;  also  State 

Entomologist. 
B.  H.  Walden,  B.  Agr.,  D.  J.  Caffrey,  B.  Agr., 
A.  B.  Champlain,  Assistants. 
Miss  E.  B.  Whittlesey,  Stenographer. 


Forestry. 


Samuel  N.  Spring,  M.  F.,  Forester;  also  State 

Forester  and  State  Forest  Fire  Warden. 
W.  O.  FiLLEY,  Assistant. 
Miss  E.  L.  Avery,  Stenographer. 


Plant  Breeding. 


H.  K.  Hayes,  B.  S.,  Plant  Breeder. 
C.  D.  HuBBELL,  Assistant. 


Buildings  and  Grounds. 


William  Veitch,  In  Charge. 


IMPROVEMENT    IN    CORN 

BY 

By  H.  K.  Hayes  and  E.  M.  East. 

Introduction. 

Logically  directed  efforts  to  improve  the  general  field  crops 
-of  the  United  States  may  be  said  to  have  begun  with  the  intro- 
duction of  Vilmorin's  Isolation  Principle.  This  principle  uses 
the  average  character  of  a  plant's  progeny  as  an  index  of  that 
particular  plant's  productiveness.  When  applied  to  corn  breed- 
ing the  method  is  commonly  known  as  the  "ear  to  row  method," 
and  consists  in  growing  a  large  number  of  selected  ears  in  such 
a  way  that  the  yield  of  each  ear  may  be  compared  with  that  of 
every  other  ear.  Thus  if  twenty  ears  are  to  be  compared,  a 
plot  of  uniform  soil  is  selected  in  which  twenty  rows  of  equal 
length  are  marked  out.  In  each  of  these  rows  the  seeds  from 
a  single  ear  are  planted.  The  crop  from  each  row,  harvested 
and  weighed  separately,  is  the  basis  upon  which  selections  are 
made,  and  seed  is  saved  only  from  those  rows  which  have  proved 
.the  better  yielders  by  this  actual  field  test.  Many  low  yielding 
ears  produce  some  progeny  which  are  as  handsome  in  appear- 
ance as  any  which  grow  in  the  high  yielding  rows  but  these  are 
invariably  discarded  because  they  come  from  strains'  which 
have  proved  their  inability  to  produce  an  average  of  high-yielding 
progeny. 

Continued  selection  by  this  method  yielded  very  promising 
results  with  corn  during  the  early  years  of  its  application,  but 
the  later  generations  failed  to  fulfil  this  promise.  Definite 
reasons  for  this  comparative  failure  in  the  corn  breeding  work 
•of  the  United  States  can  now  be  given,  for  within  the  last  few 
years  investigators  have  arrived  at  some  understanding  of 
the  underlying  principles  concerned.  These  principles  are 
yet  but  imperfectly  understood,  but  they  are  sufficiently  clear 
to  show  that  practical  corn  breeding  must  undergo  a  radical 
change  in  method  if  it  is  to  take  advantage  of  the  full  possibil- 
ities which  lie  open  to  it.     The  purpose  of  this  bulletin  is  to  out- 


4  CONNECTICUT    EXPERIMENT    STATION,     BULLETIN    1 68 

line  these  possibilities  in  the  light   of  the  most  recent  investi- 
gations of  the  subject. 


The  Two  Results  Attending  the  Formation  of  a  Seed. 

Our  field  crops  as  a  rule  form  seed  only  after  the  fertilization 
of  the  female  reproductive  cells  —  the  egg  cells  —  by  male 
reproductive  cells  contained  in  the  pollen  grains.  In  corn, 
for  example,  a  single  pollen  grain  alighting  upon  a  silk  germinates 
and  grows,  forming  a  tube  which  reaches  the  ovary.  Through 
this  pollen  tube  the  male  cell  is  carried  until  it  reaches  the  ovule. 
There  it  fuses  with  the  egg  cell  and  fertilization  is  accomplished. 
The  final  result  of  such  fertilization  is  a  mature  seed  which 
under  proper  conditions  grows  into  a  new  plant. 

This  fertilization  effects  two  very  different  results:  first,  a 
union  of  the  hereditary  characters  possessed  by  the  parents; 
second,  a  stimulation  to  the  cell  division  necessary  for  normal 
development. 

Since  the  rediscovery  of  Mendel's  Law  in  1900  our  knowledge 
of  the  first  process,  —  the  transmission  of  parental  characters 
—  has  been  greatly  increased.  It  has  been  clearly  proved  that 
a  plant  or  animal  does  not  transmit  its  characteristics  as  if 
the  entire  organism  were  the  unit,  but  rather  that  its  various 
characters  are  inherited  separately.  Each  heritable  character 
behaves  as  if  it  were  represented  by  some  special  structure 
found  in  the  reproductive  cells.  Such  characters  are  known 
as  "unit"  characters.  If  a  plant  breeds  true  for  one  of  these 
characters,  its  "unit"  must  have  been  received  from  both  of 
the  parents.  If  two  plants  are  crossed  one  of  which  lacks  the 
character,  however,  then  the  plant  is  hybrid  for  that  character; 
and,  when  its  germ  cells  are  formed  half  of  them  possess  the 
character  and  half  are  without  it.  Among  the  progeny  of 
the  plant,  therefore,  are  found  individuals  of  each  kind. 

A  cross  between  two  corn  varieties  will  illustrate  this  matter. 
If  a  sugar  corn  is  crossed  with  a  starchy  corn,  such  as  a  flint  or 
dent,  there  is  produced  a  hybrid  seed  of  a  starchy  nature  which 
cannot  be  distinguished  from  seeds  of  the  starchy  parent.  It 
matters  not  which  variety  is  the  female  parent.  On  growing 
the   hybrid   seeds   the  following   year   and   self-fertilizing    the 


INHERITANCE    OF    CHARACTERS  5 

plants/  ears  are  produced  which  have  on  the  average  three 
starchy  seeds  to  one  sugar  seed.  These  results  may  be  under- 
stood by  the  use  of  the  following  scheme. 

The  starchy  corn  produced  in  all  of  its  reproductive  cells 
some  substance  which  caused  starch  to  be  formed.  This  sub- 
stance may  be  represented  by  the  capital  letter  S.  The  sugar 
corn  lacked  this  substance  and  therefore  wrinkled  sugar  com 
resulted.  The  lack  of  the  starchy  factor  may  be  represented 
by  the  small  letter  s.  Therefore  the  difference  between  starchy 
and  sugar  com  is  the  presence  or  absence  of  the  starchy  factor. 
On  crossing  the  starchy  and  sugar  varieties,  leaving  out  of 
consideration  all  other  characters,  —  one  can  easily  see  that  in 
each  case  there  will  be  a  union  of  two  reproductive  cells,  one 
of  which  contains  S  and  the  other  s.  -  In  some  cases  it  is  neces- 
sary to  receive  the  character  from  each  parent  for  it  to  develop 
properly.  When  received  from  only  one  parent  it  develops 
only  partially  and  the  hybrid  has  what  appears  to  be  an  inter- 
mediate condition.  In  the  case  under  consideration  one  "dose" 
is  sufficient  and  the  hybrid  seed  is  completely  starchy.  In 
instances  of  this  kind  the  character  is  said  to  be  completely 
dominant. 

The  reproductive  cells  produced  by  these  crossed  plants  are 
of  two  kinds,  one  half  containing  S  (the  unit  causing  starchiness) 
and  the  other  half  containing  s  (the  unit  causing  sugariness) 
and  may  be  represented  as  follows: 

Male  reproductive  cells,  S+s. 
Female  reproductive  cells,  S+s. 
A  chance  union  of  these  cells  will  give  the  following  results 
and  ratios,  1  SS  :  2  Ss  :  1  ss.  As  the  SS  and  Ss  forms  look  alike 
we  will'  obtain  starchy  and  sugar  seeds  in  the  ratio  of  three  to 
one.  Those  seeds  without  starchiness,  the  ss  forms,  will  breed 
true  to  the  sugar  type;  the  Ss  kernels  being  hybrid  will  again 
produce  both  starchy  and  sugar  corn  in  the  ratio  of  three  to 
one;  and  the  SS  kernels  will  produce  corn  all  of  the  starchy  type. 

Thus  we  see  that  when  a  character  has  been  received  from 
both  the  male  and  female  reproductive  cells  —  that  is,  in  double 
dose  —  it  will  breed  true.     Such  a  character  is  said  to  be  in  a 


1  By  self-fertilization  is   meant  the  fertilization  of  the  egg  cells  of  a 
plant  by  its  own  pollen  grains. 


6  CONNECTICUT    EXPERIMENT    STATION,     BULLETIN    l68 

"homozygous"  condition.  When  a  character,  however,  is 
found  in  only  half  of  the  reproductive  cells  it  is  said  to  be  in 
a  "heterozygous"  condition  and  progeny  of  different  types  are 
produced.  This  principle  shows  the  reason  why  among  sister 
seeds  or  sister  plants  alike  in  appearance  some  produce  plants 
of  one  nature  while  others  produce  progeny  with  different 
characteristics.  Furthermore,  this  alternative  inheritance, 
which  is  very  widespread  if  not  universal,  is  of  the  utmost 
importance  in  obtaining  combinations  of  desirable  characters; 
since  one  may  cross  two  varieties  each  having  desirable  qual- 
ities and  may  rest  assured  that  they  will  reappear  in  the  grand- 
children^  in  all  possible  combinations  even  though  they  may 
appear  to  have  been  blended  in  the  hybrids. 

The  stimulus  to  development  due  to  fertilization  should  not 
be  confused  with  the  union  of  parental  characters.  It  is  believed 
to  be  due  to  the  bringing  in  to  the  egg  cell  of  some  necessary 
chemical  element  by  the  male  reproductive  cell.  Probably  in 
every  case  where  fertilization  can  take  place  at  all  there  is  a 
certain  amount  of  this  stimulus  to  development,  but  the  thing 
of  special  interest  to  corn  growers  is  that  this  stimulus  to  devel- 
opment is  far  greater  in  a  hybrid  than  it  is  in  a  pure  bred  variety. 

The  fact  that  a  cross  between  two  varieties  is  more  vigorous 
in  its  first  generation  than  a  self  fertilized  type  has  been  alluded 
to  by  many  scientists.  Darwin  in  his  "Cross"  and  Self-fertil- 
ization in  the  Vegetable  Kingdom"  gives  many  examples  of 
such  increased  vigor.  Mendel,  the  discoverer  of  the  only- 
known  law  of  heredity  mentions  the  fact  that  a  first  generation 
hybrid  between  two  of  his  sweet  pea  types  grew  more  vigorously 
and  to  a  greater  height  than  either  parent.  As  this  fact  had 
been  known  for  so  many  years  it  seems  strange  that  it  has  not 
been  more  widely  used  in  practical  work,  yet  perhaps  this 
was  because  the  precise  action  of  selection  was  then  unknown. 

What  Selection  Does. 

Selection  by  man  may  be  said  to  acomplish  simply  the  iso- 
lation from  the  commercial  variety  of  those  particular  types 


2  In  certain  special  cases  of  sexlimited  inheritance  in  animals  and 
probably  similar  phenomena  in  plants,  there  are  apparent,  but  not  real 
exceptions  to  this  rule. 


WHAT    SELECTION    DOES  7 

which  prove  of  the  greatest  promise  from  the  business  point 
of  view.  With  every  precaution  to  prevent,  therefore,  selection 
tends  toward  inbreeding.  As  we  have  seen,  it  is  only  when  a 
character  unit  is  found  pure  in  both  the  male  and  female  repro- 
ductive cells  that  it  produces  progeny  all  of  which  exhibit  this 
same  character.  As  selection  aims  to  produce  a  variety  in 
which  all  the  characters  are  uniform,  it  is  easy  to  see  how  the 
application  of  the  selection  principle  tends  toward  inbreeding. 
Selection  can  not  make  new  types  but  simply  isolates  the  vari- 
ations produced  by  nature.  Just  how  this  is  accomplished  is 
not  apparent  until  one  sees  clearly  that  variations  are  not  all 
alike. 

There  are  two  main  classes  of  variations: 

1.  Fluctuating  variations,  those  which  are  due  solely  to 
surrounding  influences,  such  as  better  position  for  development 
or  increased  fertility.     Such  variations  are  not  inherited. 

2.  Inherited  variations,  those  due  to  some  structure  of  the 
reproductive  cells,  which  may  depend  on  environmental  con- 
ditions for  their  full  development,  but  not  for  their  transmission. 
Only  these  variations  are  of  value  as  bases  for  selection. 

The  experiments  of  Johannsen,  a  Danish  plant  physiologist, 
which  have  later  been  corroborated  by  many  other  investigators 
with  very  different  experimental  material,  have  given  the  correct 
interpretation  of  this  matter.  Johannsen  worked  with  beans. 
In  one  of  his  experiments  the  weight  of  individual  beans  was 
the  subject  under  consideration.  When  the  larger  beans  from 
a  commercial  variety  were  selected  as  seed  Johannsen  found 
that  the  average  size  of  the  beans  could  be  increased.  If, 
however,  different  types  (that  is,  inherited  variations)  were 
first  isolated  by  inbreeding;  then  selection  of  larger  or  smaller 
beans  (fluctuating  variations)  had  no  effect  on  the  progeny. 
In  both  cases  the  average  of  the  progeny  continued  true  to  the 
type  or  average  of  the  isolated  pure  race.  Similarly,  almost  all 
commercial  varieties  are  mixtures  of  types,  and  the  sole  result 
of  selection  is  to  isolate  pure  types  from  such  mixtures. 

In  a  naturally  cross-fertilized  species  like  corn  it  is  more 
difficult  to  isolate  pure  types  by  the  application  of  Vilmorin's 
Selection  Principle  than  in  species  where  self-fertilization  is 
the  rule.  Certain  results  of  the  Illinois  Agricultural|Experiment 
Station,  however,  indicate  that  such  a  result  is   possible.      For 


8  CONNECTICUT    EXPERIMENT    STATION,     BULLETIN     l68 

example,  after  selecting  ears  with  high  oil  content  for  a  period 
of  six  years,  the  average  oil  content  was  increased  from  4.70%' 
to  6.50%.  At  this  time  selections  were  made  from  this  high 
oil  strain  for  an  entirely  different  purpose.  After  this  new 
strain  had  been  grown  in  an  isolated  plot  for  a  period  of  six 
years,  during  which  time  no  selections  for  oil  content  had  been 
made,  there  was  found  to  be  no  appreciable  loss  in  oil  content. 
The  difference  in  the  difficulties  encountered  by  the  selectionist 
in  cross-fertilized  and  in  self-fertilized  species  will  perhaps  be 
made  clearer  by  illustrations,  and  it  happens  that  two  of  Con- 
necticut's most  important  agricultural  crops,  corn  and  tobacco, 
are  admirably  suited  for  the  purpose. 

Comparison  of  the  Effect  of  Selection  upon  Corn  and  Tobacco. 

Tobacco  is  an  example  of  what  ma}^  be  called  a  close-fertilized 
species,  as  the  tobacco  flower  is  naturally  arranged  for  self- 
fertilization.  Because  of  this  fact  it  is  a  comparatively  easy 
matter  to  isolate  the  best  types  of  tobacco  from  the  commercial 
iield  and  to  breed  only  from  them.  The  reason  for  the  marked 
similarity  of  different  fields  of  tobacco  without  doubt  is  due  to 
a  conscious  or  unconscious  selection  of  the  types  which  were 
best  adapted  to  the  conditions  encountered,  and  because  the 
nature  of  the  species  has  allowed  the  easy  elimination  of  the 
poorer  types. 

Indian  corn,  on  the  other  hand,  is  naturally  arranged  for 
cross-fertilization;  the  male  and  female  organs,  that  is,  tassels 
and  silks,  are  borne  on  widely  separated  parts  of  the  plant. 
This  fact  combined  with  the  enormous  production  of  pollen 
miakes  cross-fertilization  through  the  agency  of  wind  an  exceed- 
ingly common  thing.  And  since  an  immediate  cross  between 
two  types  is  more  vigorous  and  productive  than  either  type  in 
a  pure  state,  when  the  best  ears  are  selected  from  a  field  one 
is  much  more  likely  to  select  those  which  are  in  a  hybrid  con- 
dition and  which  will  not  breed  true  in  later  generations.  This 
is  one  reason  why  so  many  different  varieties  of  corn  are  in  ex- 
istence today.  It  is  one  reason  why  such  diverse  types  are 
found  in  a  single  field.  It  is  the  reason  why  constant 
selection  gives  more  uniform  and  better  types  from  the  stand- 
point of  hereditary  characters,  but  types  which. have  lost  some- 
thing of  the  vigor  that  comes  from  hybridization. 


INCREASED    VIGOR    FROM    CROSS-BREEDING  9 

Tobacco  and  corn  may  be  compared  to  advantage  from 
another  standpoint.  Tobacco  is  of  its  greatest  value  when  it 
shows  a  marked  uniformity  and  quaHty,  both  of  which  are  of 
more  importance  than  total  yield  per  acre.  It  is  fully  recog- 
nized that  a  first  generation  hybrid  between  two  varieties  of 
tobacco  is  as  uniform  in  field  habit  as  either  parent  and  is  more 
vigorous  than  either  parent;  yet  cross  bred  tobacco  is  coarser 
and  therefore  very  inferior  in  quality  and  in  some  cases  abso- 
lutely worthless.  We  do  not  mean  to  condemn  improvement 
in  tobacco  by  hybridization;  but  careful  heredity  experiments 
have  shown  that  the  reason  for  the  apparent  lack  in  quality 
in  some  of  the  new  varieties  recently  produced  by  hybridization, 
is  due  to  the  fact  that  as  yet  they  have  not  been  selected  long 
enough  to  be  in  a  pure  condition  in  all  characters  and  therefore 
cannot  produce  uniform  quality. 

In  the  case  of  corn,  however,  the  important  fact  from  a  prac- 
tical standpoint  is  total  yield  in  bushels  of  ears  and  tons  of  stover 
per  acre.  Many  of  the  conditions  of  uniformity  demanded 
by  the  score  card  fanciers  are  of  no  importance  at  all  to  the 
commercial  grower.  Reasoning  from  this  standpoint,  three 
writers  published  articles  in  1909  suggesting  that  some  method 
for  utilizing  the  added  vigor  due  to  crossing  .should  receive 
commercial  trial.  Shull  and  East  from  their  studies  on  inher- 
itance in  maize  concluded  that  some  method  whereby  only 
first  generation  hybrids  be  grown  for  the  commercial  crop 
would  prove  of  advantage  and  materially  increase  the  present 
yield  of  corn  per  acre.  Toward  the  same  end,  Collins  collected 
evidence  showing  that  in  nearly  every  case  where  such  a  method 
had  been  tried  increased  yields  were  obtained  by  crossing. 
All  methods  now  in  use  for  the  improvement  of  corn  are  by 
the  application  of  the  selection  principle  and  tend  sooner  or 
later  toward  inbreeding.  As  corn  naturally  produces  the  best 
results  when  crossed  we  hold  that  all  methods  now  used  are 
wrong  unless  combined  with  some  method  for  continuous  crossing. 

The  Effects  of  Inbreeding  Upon  Corn. 

It  may  be  interesting  to  observe  the  actual  effect  of  the  iso- 
lation of  pure  types  upon  the  yield  of  corn.  The  data  given  in 
Table  1  show  the  effects  of  inbreeding  and  confirm  the  fact 
that  a  commercial  variety  is  composed  of  many  different  types. 


CONNECTICUT    EXPERIMENT    STATION,     BULLETIN    K 


TABLE   1. 

Effect  of  Inbreeding  on  Yield. 


Variety 

Year 

No.  Years 

Yield  in 

Grown 

Inbred 

Bushels 

Watson's  Flint,  No.  5,  Gen.  1 

1908 

75.7 

No.  5,  Gen.  2 

1909 

v 

47.5 

No.  5,  Gen.  3 

1910 

2 

36.1 

Starchy,  No.  10,  Gen.  1 

1908 

70.5 

No.  10,  Gen.  2,  Ear  1 

1909 

1 

56.0 

No.  10,  Gen.  2,  Ear  2 

1909 

1 

43.0 

No.  10,  Gen.  3,  Daughter  of 

Earl 

1910 

2 

67.0 

No.  10,  Gen.  3,  Daughter  of 

Ear  2 

1910 

2 

48.7 

Stowell's  Ev.,  No.  19,  Gen.  1 

1908 

93.2 

No.  19,  Gen.  2,  Ear  1 

1910 

l" 

53.6 

No.  19,  Gen.  2,  Ear  2 

1910 

1 

58.7 

Learning  (the  parent),  Gen.  1 

Unselected 

88.0 

No.  7,  Gen.  2 

1906 

1 

60.9 

No.  7,  Gen.  3 

1907 

2 

59.9 

No.  7,  Gen.  4 

1908 

3 

46.0 

No.  7,  Gen.  4 

1909 

3 

59.7 

No.  7,  Gen.  5,  Ear  1 

1910 

4 

63.2 

No.  7,  Gen.  5,  Ear  2 

1910 

4 

68.1 

Learning  (the  parent).  Gen.  1 

Unselected 

88.0 

No.  6,  Gen.  2 

i906 

1 

59.1 

No.  6,  Gen.  3 

1908 

2 

95.2 

No.  6,  Gen.  4 

190"9 

3 

57.9 

No.  6,  Gen.  5 

1910 

4 

80.0 

Learning  (the  parent),  Gen.  1 

Unselected 

88.0 

No.  9,  Gen.  2 

i906 

1 

42.3 

No.  9,  Gen.  3 

1908 

2 

51.7 

No.  9,  Gen.  4 

1909 

3 

35.4 

No.  9,  Gen.  5 

1910 

4 

47.7 

Learning  (the  parent).  Gen.  1 

Unselected 

88.0 

No.  12,  Gen.  2 

1906 

1 

38.1 

No.  12,  Gen.  3 

1907 

2 

32.8 

No.  12,  Gen.  4 

1908 

3 

46.2 

No.  12,  Gen.  5,  Ear  1 

1909 

4 

23.3 

No.  12,  Gen.  5,  Ear  2 

1909 

4 

28.7 

No.  12,  Gen.  6,  Daughter  of 

Ear  1 

1910 

5 

16.6 

No.  12,  Gen.  6,  Daughter  of 

Ear  2 

1910 

5 

9.5 

It  will  be  noted  that  a  column  is  given  showing  the  year  in 
which  each  selection  was  grown.  As  all  strains  were  grown  on 
the  same  plot  each  season  but  on  a  different  field  the  following 
year,  some  idea  can  be  obtained  as  to  the  effects  of  different 


INCREASED    VIGOR    FROM    CROSS-BREEDING  II 

environmental  conditions.  In  1908  the  corn  plot  was  on  very 
fertile  soil  consequently  the  yields  were  very  good.  Four 
stalks  to  the  hill  were  grown  this  season  but  as  only  three  were 
grown  in  later  years,  the  1908  results  were  reduced  one-fourth, 
or  to  a  three  stalk  per  hill  basis.  During  1909  the  season  was 
not  favorable,  consequently  the  yields  for  nearly  all  of  the 
varieties  were  smaller  than  in  1910.  For  example,  Starchy 
No.  10,  Learning  No.  6  and  Learning  No.  7,  strains  which  pre- 
sumably were  almost  pure  types,  each  gave  considerable 
increases  in  1910  over  their  yields  for  1909. 

A  study  of  this  table  brings  to  view  several  other  interesting 
facts.  In  nearly  all  cases  the  first  generation  of  inbreeding 
has  the  greatest  detrimental  effect.  It  is  also  clearly  shown 
that  after  a  type  has  been  inbred  until  it  is  in  a  pure  state 
continued  inbreeding  does  not  change  its  yielding  ability. 
Inbreeding,  therefore,  has  simply  isolated  the  different  types. 
from  the  commercial  variety.  This  last  fact  is  most  noticeable 
from  a  study  of  the  Learning  strains,  all  four  of  which  came 
originally  from  the  same  commercial  variety.  After  isolation 
by  inbreeding,  during  which  time  all  received  the  same  treat- 
ment, four  types  have  been  obtained  which  give  different  yields. 
The  shape  of  ears,  height  of  plants  and  general  fieid  characters 
are  also  different,  although  within  g,  type  they  are  very  uniform. 
One  of  these  "pure  types,"  No.  6,  gave  nearly  as  large  a  yield  as  was 
received  from  the  normal  commercial  variety  from  which  it 
was  isolated,  while  on  the  same  field  strain  No.  12  produced 
only  small  immature  ears.  Thus  one  sees  that  some  pure  strains 
are  so  inferior  that  they  can  scarcely  live  when  isolated,  but 
have  been  kept  in  existence  by  the  increased  vigor  obtained 
when  in  hybrid  combinations  with  other  types. 

Comparison  of  Pure    Types,   Crosses   Between  Pure    Types  and 
Normally  Cross-fertilized  Varieties. 

Table  2  in  which  crosses  are  compared  with  their  parents  is 
of  still  greater  practical  interest.  The  number  of  years  which  a 
type  has  been  inbred  is  given;  and,  for  convenience  the  letters  Fi 
and  F2  are  used  and  denote  respectively^the  first  and  second  hybrid 
generation.  •  Crosses  No.  (15  x  8)  and  No.  (11x8)  were  between 
varieties  which  had  not  been  inbred.     The  yield  of  the  crosses 

I 


12  CONNECTICUT    EXPERIMENT    STATION,     BULLETIN     l68 


TABLE  2. 
Crossed,  Normal  and  Selfed  Varieties  Compared. 


Comparison  in 

yield  between  the 

Variety 

Year 

No.   Yrs. 

Yield  in 

original  normal 

Grown 

Inbred 

Bushels 

fertilized  varie- 
ties and  the  cross 

Long.  Flint  No.  15 

1908 

72.0 

72.0 

111,  High  Protein  No.  8 

1908 

121.0 

121.0 

No.  (15  X  8)  Fi 

1908 

124.0 

124.0 

Sturgis'  Flint  No.  11 

1908 

48.0 

48.0 

No.  8 

1908 

121.0 

121.0 

No.  (11  X  8)  Fi 

1908 

130.0 

130.0 

No.  8 

1908 

121.0 

121.0 

Learning  No.  7 

1908 

3 

62.0 

88.0 

No.  (8  X  7)  Fi 

1908 

142.0 

142.0 

No.  7 

1910 

4 

65.5 

88.0 

Stowell's  Ev.  No.  19 

1910 

1 

53.6 

93.2 

No.  (7  X  19)  Fi 

1910 

142.7 

142.7 

Watson's  Flint  No.  5 

1909 

1 

47.5 

75.7 

No.  11 

1909 

1 

44.2 

48.0 

No.  (5  X  11)  Fi 

1909 

76.3 

76.3 

No.  5 

1909 

1 

47.5 

75.7 

Learning  No.  6 

1909 

3 

57.9 

'    88.0 

No.  (5  X  6)  Fi 

1909 

88.9 

\              92.2 

No.  (5  X  6)  Fi 

1910 

105.5 

/ 

No.  (5  X  6)-l  Fs 

1910 

1 

54.1 

\             51.5 

No.  (5  X  6)-8  F2 

1910 

1 

48.9 

/ 

Starchy  No.  10 

1910 

2 

48.7 

70.5 

Learning  No.  6 

1910 

4 

80.4 

88.0 

No.  (10  X  6)  Fi 

1910 

139.0 

139.0 

Learning  No.  12 

1909 

3 

35.4 

88.0 

Learning  No,  9 

1909 

4 

23.3 

88.0 

No.  (12  X  9)  Fi 

1909 

110.2 

\           113.8 

No.  (12  X  9)  Fi 

1910 

117.5 

/ 

No.  (12  X  9)-l  F2 

1910 

1 

102.2 

1 

No.  (12  X  9)-4  F2 

1910 

1 

91.5 

\             98.4 

No.  (12x9)-12  F2 

1910 

1 

91.5 

J 

is  compared  with  that  of  the  parents,  all  having  been  grown 
-on  the  same  field.  Increases  of  3  bushels  per  acre  in  the  first 
•€ase  and  of  9  bushels  per  acre  in  the  second  were  received  in 
favor  of  the  cross  over  the  better  yielding  parent.  The  cross 
b)etween  No.  8  and  No.  7  shows  an  increase  for  the  cross  of  21 
'bushels  per  acre  over  the  naturally  open  field  pollinated  parent 
which  gave  the  highest  yield.  The  remainder  of  the  crosses 
are   between  inbred   types   which   are  relatively   pure.     Large 


INCREASED    VIGOR    FROM    CROSS-BREEDING  IJ, 

increases  are  received  from  such  crosses.  In  order  to  have  a 
standard  of  comparison  other  than  that  between  the  inbred 
varieties  and  their  hybrids  and  a  standard  of  greater  commercial 
importance  a  column  has  been  added  to  the  table,  comparing  the 
cross  between  two  inbred  types  with  the  yield  of  the  original 
variety  from  which  the  types  were  isolated.  Increases  of 
from  6  bushels  to  59  bushels  were  obtained  in  favor  of  the 
cross  over  the  better  3delding  parent,  the  average  for  the  five- 
crosses  so  considered  being  31  bushels. 

Another  important  fact  which  is  shown  by  this  table  is  that. 
the  F2  generation  gives  a  much  smaller  yield  than  the  Fi  gene- 
ration. The  Fi  generation  of  the  cross  between  No.  5,  Watson's. 
White  Flint  and  No.  6,  a  Leaming  strain,  produced  at  the  rate 
of  105.5  bushels  per  acre,  while  the  F2  generation  grown  on  the 
same  field  produced  only  51.5  bushels  per  acre.  The  Fi  gene- 
ration of  the  cross  No.  (12x9),  between  two  Leaming  strains, 
produced  at  the  rate  of  117.5  bushels  per  acre,  although  the- 
F2  generation  yielded  at  the  rate  of  only  98.4  bushels. 

These  data  show  that  the  greatest  stimulus  to  development 
from  crossing  two  distinct  types,  is  obtained  only  in  the  first 
hybrid  generation.  Therefore  practical  utilization  of  the  total 
increase  in  vigor  due  to  crossing  is  possible  only  when  the  first, 
hybrid  generation  is  the  commercial  crop.  This  necessitates 
making  the  cross  each  year.  The  explanation  of  the  decrease 
in  vigor  in  the  second  hybrid  generation  is  exactly  the  same 
as  the  explanation  of  the  apparent  deterioration  when  corn 
is  inbred.  Both  are  caused  by  recombinations  of  characters 
among  which  some  "ptire  type"  individuals  are  obtained. 
In  inbreeding  the  apparent  deterioration  is  more  marked  because 
the  percentage  of  such  individuals  is  likely  to  be  much  greater. 

Comparisons   Between    Varieties  and  First  Generation   Hybrids. 

It  is  realized  that  if  the  theory  that  germ-cell  purity  for  certain 
characters  causes  purity  of  type  is  correct,  and  it  has  stood 
the  test,  then  theoretically  the  best  yielding  commercial  type 
of  com  could  be  produced  by  a  cross  between  two  selected 
inbred  types  which  when  mated  proved  the  -most  vigorous,  a 
plan  proposed  by  Shull.  The  cost  of  producing  seed  by  first 
isolating  pure  types  and  then  crossing  them  would  be  very  great,. 


14 


CONNECTICUT    EXPERIMENT    STATION,     BULLETIN    l( 


however,  and  the  method  could  be  used  only  by  persons  willing 
to  spend  the  necessary  time  and  study,  first  to  isolate  the  pure 
types  and  then  to  find  out  the  best  yielding  combination.  In 
order  to  lessen  the  risk  of  losing  the  best  pure  types  a  very  large 
number  would  have  to,  inbred  for  several  years.  After  this 
work  was  finished  it  would  still  be  necessary  to  make  all  possible 
hybrid  combinations  between  them.  A  few  seedsmen  with 
large  resources  might  be  able  to  accomplish  this  successfully 
and  profitably,  but  it  does  not  appear  to  be  practicable  for  the 
general  corn  grower.     For  him  we  suggest  another  plan. 

There  are  in  Connecticut  many  varieties  of  corn  which  have 
been  grown  in  the  same  locality  for  long  terms  of  years  and  which 
have  been  continually  selected  toward  some  particular  type. 
These  varieties  are  comparatively  pure,  and  it  is  practically 
certain  that  by  testing  out  crosses  between  them  various  com- 
binations can  be  found  which  will  greatly  increase  the  average 
yield  per   acre.     The   operation  of  crossing  is   a  very  simple 


TABLE  3. 
Results  of  Morrow  and  Gardner's  Experiments  at  The  Illinois 
Experiment  Station  in  1892, 


Variety 

No.  Ears 
Received 

Bushels   of   Air 
Dry  Corn 

Burr's  White 
Cranberry 
Average 
Cross 

9960 
9200 
9580 
7080 

64.2 
61.6 
62.9 
67.1 

Burr's  White 
Helm's  Improved 
Average 
Cross 

9960 
10880 
10420 
11000 

64.2 
79.2 
71.7 
73.1 

Leaming 
Golden  Beauty 
Average 
Cross 

10440 
8280 
9360 

11520 

73.6 
65.1 
69.3 

86.2 

Chanpiom  White  Pearl 

Leaming 

Average 

Cross 

11080 

10440 

10760 

8760 

60.6 
73.6 
76.1 

76.2 

Burr's  White 
Edmonds 
Average 
Cross 

9960 

9040 

9600 

10400 

64.2 
58.4 
61.3 

78.5 

PLAN    FOR    PRODUCING    HYBRID    SEED  15 

matter  and  can  easily  be  carried  out  by  each  farmer  for  himself. 
Furthermore,  nearly  all  of  these  crosses  will  give  a  yield  suffi- 
ciently greater  than  either  of  the  two  parents  to  pay  the  farmer 
for  his  trouble. 

The  only  previous  work  of  just  this  kind  known  to  us  is  that 
■of  Morrow  and  Gardner  at  the  Illinois  Experiment  Station 
which  was  first  reported  in  1892.  Bulletin  25  entitled  "Field 
Experiments  with  Corn"  gives  the  results  of  five  tests  of  the 
comparative  yields  of  first  generation  hybrids  and  their  parents. 
Because  of  our  belief  in  the  value  of  crossing,  a  summary  of 
the  results  of  Morrow  and  Gardner's  tests  is  given.  Table  3 
gives  the  number  of  ears  obtained  and  the  yield  in  bushels  of 
air-dry  corn  per  acre  for  five  different  crosses.  It  shows  that  the 
yield  of  the  hybrids  in  the  five  tests  averaged  7.16  bushels 
more  than  the  average  of  the  parent  varieties  and  4.66  bushels 
more  than  the  high  yielding  parent. 

In  1893  four  additional  tests  were  reported.  Three  of  the 
four  gave  increases  over  the  average  of  the  parents,  their  average 
increase  of  yield  being  9.5  bushels  per  acre  with  an  increase  of 
2.7  bushels  per  acre  over  the  high  yielding  parent.  In  the 
fourth  test  the  cross  gave  a  decreased  yield  but  including  this 
we  find  that  the  average  increase  for  the  crosses  over  the  aver- 
age of  the  parents  was  2.5  bushels.  As  has  been  pointed  out 
by  Collins,  little  confidence  can  be  placed  in  the  results  of  these 
four  tests.  The  lack  of  uniform  conditions  during  this  test  is 
indicated  by  the  great  difference  between  the  yield  of  duplicate 
plots  of  the  different  varieties  used  in  this  experiment,  which 
Tanged  as  high  as  15  bushels  per  acre. 

In  1909  several  Connecticut  farmers  became  interested  in 
the  production  of  first  generation  hybrid  corn  in  co-operation 
with  this  Station.  A  plan  was  sent  to  the  different  co-operators 
giving  directions  for  the  production  of  crossed  seed  with  the 
idea  of  comparing  the  cross  with  its  parents  in  1910.  Only 
ten  men  from  the  thirty  who  had  intended  to  produce  hybrid 
seed  actually  carried  through  the  operation  according  to  direc- 
tions. In  1910  seven  of  these  men  gave  a  few  ears  each  of  their 
crossed  seed  and  of  one  parent  variety  to  the  Station,  which 
compared  them  on  a  level  piece  of  land  of  about  one  and  one- 
third  acres.  It  is  to  be  regretted  that  in  nearly  every  case  only 
one  parent  could  be  compared  with  the  hybrid  as  it  is  realized 


l6  CONNECTICUT    EXPERIMENT    STATION,     BULLETIN     l68 

TABLE  4. 
Comparative  Yi^ld  of  First  Generation  Hybrids  and  Their 
Parents.     Station  Test. 


that  this  does  not  give  an  accurate  determination  of  the  value 
of  the  cross.  However,  some  interesting  facts  are  shown  by 
these  tests  which  confirm  our  beHef  in  the  efficacy  of  such 
methods.  The  yields  were  determined  from  the  stand  of  corn 
and  not  from  the  size  of  the  plots.  This  fact  is  mentioned  and 
the  comparative  stand  is  given  in  Table  4,  for  if  this  test  is 
used  as  a  comparison  of  the  different  varieties,  it  is  realized 
that  the  corn  which  germinated  poorest  has  an  advantage  of 
increased  room  over  the  better  germinating  varieties.  The 
seed  was  not  received  early  enough  to  test  its  germinating 
qualities  and  four  kernels  were  planted  per  hill,  the  plants 
being  thinned  to  three  per  hill  at  the  first  cultivation.  It 
will  be  noted  that  in  nearly  every  case  the  cross  was  as  tall  as 
the  parent  used.  An  exact  study  of  crosses  between  varieties 
differing  widely  in  height  proves  a  first  generation  hybrid  is 
not  uniformly  as  tall  as  the  taller  parent,  but  the  results  show 


LARGER    YIELDS    FROM    HYBRID    SEED 


17 


that  a  first  generation  hybrid  is  always  taller  than  the  average 
height  of  the  parents.  The  results  also  show  an  intermediate 
time  of  maturity  in  the  hybrid  as  compared  with  the  parent 
varieties;  and  while  no  exact  figures  can  be  given,  it  is  believed 
that  the  hybrid  matures  earlier  than  the  average  date  of  maturity 
of  the  parents.  The  reason  for  this  is  that  increased  vigor  due 
to  crossing  is  often  shown  by  rate  of  growth  as  well  as  by  actual 
size  attained. 

The  yield  of  corn  was  taken  at  husking  time  and  with  the 
exception  of  the  cross  between  Stadtmueller's  Learning  and 
Reid's  Yellow  dent,  which  was  in  poor  condition,  is  believed  to 
be  a  fairly  accurate  comparison.  This  cross  was  also  tested 
by  Mr.  Stadtmueller  who  received  4}/^  bushels  more  per  acre 
for  the  cross  than  for  the  parent  grown. 

The  Brewer's  Dent  x  Early  Dent  cross  is  worthy  of  special 
mention.  This  cross  was  made  by  Pinney  of  Suf field,  who 
obtained  very  few  good  ears  as  the  Early  Dent  tasseled  much 
earlier  than  the  Brewer's  dent.     A  comparison  of  the  yields 


TABLE  5. 

Comparative  Yields  of  Parent  and  First  Generation  Hybrid. 

Farmers'  Tests. 


Name  of  Farmer 

Variety 

Acreage 
in  sq.  ft. 

Bu.  per 
Acre 

G.  A.  Cook 

Rhode  Island  White  Flint 
R.    I.    W.    F.    X    Mammoth 
White  Flint               / 

6000 
6000 

49.6 
62.1 

E.  M.  Ives 

Ives  Flint 

Long.  Flint  x  I.  F. 

Ives  Flint  x  Long.  Flint 

9376 
13280 
66400 

66.8 
68.1 
60.1 

G.  W.  Woodbridge 

Woodbridge's  Yellow  Flint 
Watson's  White  Flint  x  W. 
Y.  F. 

8844.5 
8844.5 

69.5 

86.7 

F.  H.  Stadtmueller 

Stadtmueller's  Leaming 
S.  L.  X  Reid's  Yellow  Dent 

66.5 
71.0 

*0.  S.  Olmstead 

Canada  Improved  Flint 
C.  I.  F.  X  Conn.  Top  Over 
Flint 

6321 
9114 

144.6 
117.0 

*  These  varieties  were  grown  on  different  fields,  and  the  yield  is  given 
in  measured|bushels.  Compare  with  the  Station  test  which  shows  a 
distinct  advantage  for  this  cross.  Mr.  Olmsted  was  pleased  with  this 
cross  and  intends  to  make  it  again. 


l8  CONNECTICUT    EXPERIMENT    STATION,     BULLETIN    l68 

received  gives  an  increase  of  17.1  bushels  for  the  cross  over  the 
Brewer  dent,  as  well  as  an  earlier  date  of  maturity.  A  cross 
similar  to  the  latter  one  gives  promise  of  being  of  value  for 
silage  purposes,  as  large  size  can  be  thus  combined  with  an 
earlier  date  of  maturity.  Such  a  cross  could  be  made  by  plant- 
ing the  early  inaturing  parent  about  a  week  later  than  the 
later  maturing  variety. 

Considering  the  seven  crosses  together  we  find  that  five 
proved  beneficial,  showing  a  crop  ranging  from  7  bushels  to 
44  bushels  more  for  the  hybrid  than  for  the  parent  grown.  The 
two  crosses  which  proved  no  better  than  the  parent  variety 
were  also  tested  by  the  farmers  who  made  them.  Mr.  Wood- 
bridge's  test  of  the  Watson's  white  flint  x  Woodbridge's  flint 
gave  a  much  larger  yield  for  the  crossed  type  than  for  the  Wood- 
bridge  flint  parent.  As  may  be  seen  in  Table  5,  the  hybrid 
out3delded  the  one  parent  by  17.2  bushels  per  acre.  The  Ives  x 
Longfellow  cross  and  its  reciprocal  gave  about  the  same  yield 
as  the  Ives  parent  and  proved  of  no  benefit. 

We  may  conclude,  therefore  that  as  a  rule,  the  production 
of  corn  by  utilization  of  the  increased  vigor  due  to  a  first  gene- 
ration hybrid,  is  of  commercial  importance  and  is  worthy  of 
further  trial.  It  is  very  much  to  be  desired  that  the  matter  be 
thoroughly  tested,  and  the  Station  will  be  glad  to  co-operate 
with  other  farmers  in  the  work. 

Some  crosses  may  not  prove  more  vigorous  than  either  parent, 
but  we  will  wish  to  know  which  combinations  are  of  this  kind. 
The  reason  is  that  some  ^varieties  are  now  in  a  state  of  hybridity. 
Such  varieties  have  already  all  the  growth  stimulus  possible,  hut 
do  not  produce  high  because  they  have  poor  types  in  combination. 
In  other  words  these  varieties  with  the  stimulus  due  to  crossing 
are  only  equal  to  some  other  varieties  without  this  stimulus. 

Method  oj  Producing  Cross  Bred  Seed. 

The  first  important  step  in  the  production  of  crossed  seed 
is  the  selection  of  the  parent  varieties.  Two  varieties  should 
be  selected  that  have  been  grown  for  a  number  of  years  in  the 
same  locality  and  are  of  the  type  desired.  Such  varieties 
should  be  comparatively  pure  and  will  give  better  results  than 
those  that^ihave  never  received  attention  as  regards  selection. 


METHODS    OF    PRODUCING    CROSS-BRED    SEED  1 9 

Another  point  is  to  select  varieties  that  mature  at  about  the  same 
season,  as  otherwise  the  pollen  of  one  will  be  shed  before  the 
silks  of  the  other  appear.  The  varieties  which  will  give  best 
results  when  crossed,  however,  can  only  be  determined  by 
actual  test.  As  nearly  every  test  so  far  has  shown  as  good,  and 
generally  better,  results  for  the  hybrid  than  for  the  better 
parent,  the  selection  of  varieties  by  test  which  will  prove  most 
beneficial  will  not  cause  any  actual  loss,  even  if  the  best  com- 
bination is  not  obtained  at  the  first  test. 

If  it  is  desired  to  have  the  corn  of  a  uniform  color,  varieties 
with  a  white  and  yellow  endosperm  should  not  be  crossed 
together  as  the  grains  will  be  of  different  colors  in  the  year  follow- 
ing the  cross.  Unlike  many  plants  the  endosperm  color  varie- 
ties of  corn  show  an  immediate  effect  due  to  crossing.  For 
example  if  a  white  corn  is  crossed  with  yellow,  no  matter  which 
is  used  as  the  female  parent  the  immediate  result  is  yellow. 
If  this  seed  is  used  the  next  year,  the  year  in  which  beneficial 
results  may  be  expected  from  crossing,  white  and  yellow  seeds 
will  be  found  on  the  same  ears.  It  is  not  believed  that  the 
color  necessarily  changes  the  composition  of  the  corn,  but  for 
the  sake  of  uniformity  white  and  yellow  crosses  are  not  so 
desirable  as  those  between  like  colors. 

A  flint-dent  cross  will  be  comparatively  uniform  in  the  first 
generation  because  the  property  of  flintiness  or  dentness  is  a 
plant  character  due  to  the  amount  of  hoiiiy  starch  in  the  endosperm, 
and  is  not  immediately  affected  by  crossing.  To  illustrate, 
no  matter  which  is  used  as  the  female  parent,  no  effect  will  be 
noticed  the  year  in  which  the  cross  is  made.  The  first  hybrid  gener- 
ation will  not  be  appreciably  more  variable  than  the  parent  varie- 
ties and  will  be  more  like  the  dent  parent. 

There  are  in  Connecticut  many  good  varieties  of  both  dent 
and  flint  types  and  good  results  will  without  doubt  be  obtained 
by  crosses  between  different  flint  corn  types  for  the  flint  corn 
grower  and  crosses  between  dent  varieties  for  the  dent  corn 
grower. 

The  actual  production  of  crossed  seed  is  an  easy  matter  and 
with  a  little  attention  can  be  done  on  any  farm.  The  seed  plat 
should  be  in  an  isolated  place  at  some  little  distance  from  the 
commercial  corn  field.  The  following  diagram  illustrates  the 
method  to  be  used. 


20  CONNECTICUT    EXPERIMENT    STATION,     BULLETIN    l68 


Plat  1 


Plat    2 


D   D    D    D    D 


C   D    G    D    C    D     C     D 


Plant  the  varieties  in  alternate  rows  in  Plat  1,  all  of  one 
variety  as  C  being  planted  in  the  odd  rows  and  the  other  variety, 
D,  in  the  even  rows.  Detassel  all  of  one  variety  as  D.  This 
detasseled  variety  should  be  also  grown  in  another  isolated  plat, 
Plat  2.  Suppose  it  is  determined  to  use  D  as  the  female  variety, 
detassel  all  of  D.  The  following  results  will  then  be  obtained 
at  harvest. 

Plat  1.  D  will  be  cross  pollinated. 

Plat  1.  C  will  be  self-pollinated  or  close-pollinated. 

Plat  2.  D  will  be  self -pollinated  or  close-pollinated. 
The  detasseling  should  be  done  before  any  of  the  pollen  is 
shed  and  may  be  very  easily  accomplished  by  taking  firmly 
hold  of  the  young  tassel  and  giving  it  a  steady  upward  pull. 
In  order  to  detassel  all  of  a  variety  it  will  be  necessary  to  go 
over  the  field  several  times  at  intervals  of  a  day  or  two.  It 
is  important  to  have  all  of  the  variety  detasseled  before  the 
shedding  of  its  pollen.     If  the  varieties  differ  in  date  of  tasseling 


METHODS    OF    PRODUCING    CROSS-BRED    SEED  2  1 

it  is  recommended  that  the  variety  which  tassels  first  be  used 
for  the  female  parent,  as  the  silks  are  receptive  as  a  rule  for  a 
longer  time  than  during  the  shedding  of  the  pollen.  If 
the  varieties  do  not  differ  in  the  date  of  maturity,  seed  may  be 
obtained  by  the  following  plan  which  will  necessitate  the  using 
of  only  one  plat.  To  illustrate  by  the  use  of  the  diagram  for 
Plat  1.  Reserve  some  seed  of  C;  detassel  all  of  C  this  year. 
On  the  following  year  use  the  reserved  seed  of  C  and  the  open 
pollinated  seed  of  D  for  the  seed  plot,  using  D  this  year  for 
the  female  parent  and  reserving  enough  of  D  for  the  following 
year. 

We  recommend,  no  matter  what  method  is  used  for  pro- 
ducing the  seed,  that  in  the  first  year  seed  of  both  parent  varieties 
be  kept  on  hand  and  that  a  commercial  test  of  the  crossed  seed 
and  the  parents  be  made  in  order  to  determine  the  value  of 
the  particular  cross.  If  the  cross  proves  to  be  a  good  one, 
one  of  the  above  outlined  methods  may  be  used  for  the  yearly 
seed  plat. 


PLATE   I. 


a.     Stadtmueller's  Learning.     This  is  a  good  Connecticut  variety. 


b.     Hopson's  Longfellow.     This  corn  breeds  very  true  to  type. 


PLATE    II. 


The  middle  ear  is  the  result  of  an  immediate  cross  between  a 
white  and  yellow  variety,  and  the  ear  at  the  right  shows  what 
would  be  obtained  if  such  parents  were  used  to  produce  a 
first  generation  hybrid. 


At  the  left  and  right  of  the  photograph  are  shown  respectively 
No.  15,  Longfellow  Flint  and  No.  8,  111.  High  Protein  Dent. 
The  two  central  ears  represent  the  first  generation  hybrid. 
This  is  the  first  cross  of  Table  II. 


PLATE    III. 


a.     A  comparison  of  pure  lines  and  the    F^    and   Fg    generations. 
All  were  grown  on  the  same  field.     (Photo  by  Walden). 


At  the  right  average  of  the  parents  after  three  generations  of 
inbreeding.  At  the  left  crop  of  first  generation  cross  of  the 
inbred  strains. 


PLATE    IV. 


Outer  ears  inbred  four  generations.     Middle  ear  result  of  their 
crossing,  first  generation. 


h.     Outer  ears  inbred  one  generation, 
crossing,  first  generation. 


Middle  ear  result  of   their 


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